EP0137871B1

EP0137871B1 - Cleaning compositions

Info

Publication number: EP0137871B1
Application number: EP83306238A
Authority: EP
Inventors: Peter Carlton; Derek Davison; William John Hugh Finch
Original assignee: Procter and Gamble Ltd; Procter and Gamble Co
Current assignee: Procter and Gamble Ltd; Procter and Gamble Co
Priority date: 1983-10-14
Filing date: 1983-10-14
Publication date: 1989-10-18
Also published as: ATE47423T1; DE3380736D1; EP0137871A1

Abstract

Single phase aqueous liquid detergent compositions having a viscosity of > 180 centipoises at 20 DEG C are provided by amine oxide - anionic surfactant systems in which the total surfactant level is not more than 3.0% by weight and in which the proportion of amine oxide and anionic surfactant is in the range 80:20-99.9:0.1, more preferably 93.5:6.5-99.0:1.0, percent by weight, the compositions also comprising one or more ionisable non surface active organic or inorganic compound in an amount to give an ionic strength of at least 3.5 moles/dm<3>.

Description

This invention relates to aqueous liquid detergent compositions and more especially to aqueous hypochlorite bleach compositions of high viscosity. A thick consistency is advantageous for a liquid detergent composition, particularly one employed for cleaning hard surfaces, as the increased viscosity assists the retention of the neat composition on non-horizontal surfaces thereby enhancing the effect of the active ingredient. Viscous liquid detergent compositions are also preferred by the consumer over'thinner' products, apparently on aesthetic grounds.
High viscosity aqueous liquids can be produced in a number of ways. High concentrations of dissolved solid materials such as sugars give rise to syrups. The use of polymeric organic compounds such as gums and cellulose derivatives, that swell in aqueous media, is also a common technique used to increase viscosity. Surfactant compounds that interact with each other to produce micellar structures are also recognized as a means of thickening aqueous systems.
Examples of this surfactant micellar thickening technique, as applied to chlorine-bleach containing liquids, are disclosed in British Patent Specifications Nos. 1,329,086,1,418,671 and 1,418,672, European Published Applications Nos. 0021581 and 0030401, French Patent Applications Nos. 2,355,909 and 2,442,885 and British patent Application No. 2,003,522A. Certain of these prior art disclosures, notably European Patent Applications Nos. 0021581 and 0030401 teach the formation of liquids having viscosities of up to 1.5 · 10-⁴ m²/S at 25°C, while British Patent Specification No. 1,418,671 contemplates the preparation of aqueous media having viscosities of from 0.1 to 6 Pa - s at 20°C as an intermediate step in the formation of a liquid containing a particulate abrasive suspended in a dispersion of a filamentary network in the aqueous media. "The product viscosity disclosed by BP 1,418,671 is about 50 mPa - s.
Amine oxides are well known as components of thickened aqueous detergent compositions and are disclosed for this purpose in the above mentioned prior art. in general,the references in the art are to amine oxides in which the hydrophobic group conferring surface activity is a linear alkyl moiety but certain of the prior art disclosures, notably British Patent Application No. 2,003,522A and European 0021581 disclose the use of amine oxides in which the hydrophobic alkyl group is branched.
European Published Application No. 0079697 discloses thickened aqueous cleaning compositions containing from 0.5% to 5% of a trialkyl amine oxide as the sole surfactant, in which one alkyl group has a carbon chain length 13<R<18 and the othertwo groups are C,-C₄ alkyl, together with at least one water soluble ionisable salt in an amount to give an ionic strength of 3.0 g moles/ dm³ minimum, the compositions having a viscosity of at least 0.18 Pa - sec at 20°C. Preferred compositions comprise aqueous hypochlorite bleach compositions in which the hypochlorite itself together with the sodium hydroxide, chloride and chlorate associated with the bleach provides the, or a major part of the, ionisable compounds. Such compositions utilise a C_14―C₁₆ alkyl dimethyl amine oxide as the sole surfactant and also incorporate from 0.01 % to 0.5% by weight of the composition of a bleach stable perfume.
The Applicants have now discovered that clear, physically stable, liquid detergent compositions having low levels of surfactants (i.e. ≤3%) by weight of the composition, can be formulated to have viscosities in excess of those taught by the prior art, by means of the use of certain amine oxide-anionic surfactant combinations in which the hydrocarbyl-group conferring hydrophobicity on the amine oxide has a specific range of chain length.
Furthermore, it has been found that a degree of branching of this hydrocarbyl group is desirable and that certain branched chain alkyl amine oxides are more weight effective than the corresponding linear chain alkyl amine oxides in producing clear, stable solutions having the desired rheological properties.
According to the present invention therefore there is provided an aqueous single phase hypochlorite bleach composition having a viscosity of >0.18 Pa - s. at 20°C and comprising from 1.0% to 1.5% by weight of a surfactant system comprising a tertiary amine oxide surfactant having the formula
wherein R, is an alkyl group having an average chain length of from 14 to 16 carbon atoms which is linear or which contains no more than 70% by weight of the group of methyl or ethyl branching, and R₂ and R₃ are C,-C₄ alkyl or C_l-C₄ hydroxy alkyl together with at least one ionisable, non surface active organic, or inorganic, compound, comprising a mixture of alkali metal hypochlorite, alkali metal hydroxide and alkali metal chloride said composition incorporating from 0.01% to 0.5% by weight of the composition of a bleach stable perfume and having an ionic strength of at least 3.5 moles/dm³ wherein the surfactant consists of a mixture comprising:

a) from 93.5% to 99.5% by weight of the system of said tertiary amine oxide and from
b) 0.5% to 6.5% by weight of the system of an anionic surfactant salt incorporating an aliphatic moiety having an average carbon chain length of more than 12 and less than 18 atoms, said moiety comprising at least 40% by weight of said anionic surfactant.

In a preferred form of the invention the surfactant system comprises from 1.0% to 1.5% of a combination of a C₁₄―C₁₆ alkyl dimethyl amine oxide and an alkanoate or alkyl sulphate surfactant, the ratio of the amine oxide to anionic surfactants being within the range 19:1 to 99:1 by weight.
For the purposes of the pressnt invention viscosity is expressed as the dynamic viscosity η in Pa - s (1 Pa. s is 10 Poise). The dynamic viscosity is measured by a Brookfield RVT viscometer and for the purposes of this specification measurements are made with Spindle No. 3 at 100 rpm and a liquid temperature of 20°C. Fluid viscosity can also be expressed as the kinematic viscosity v in m²sec^-1 (1 m²sec^-1 is 10,000 stokes) as measured by an Ostwald viscometer v is characterised by the expression v=η/ρ where n is the dynamic viscosity in milli Pa - s (10-³ Pa - s) and p is the density in g/cm³. Compositions in accordance with the present invention have a density in the range from 1.10 to 1.20 g/cm³, typically approximately 1.15 g/cm³, so that the numerical value of the kinematic viscosity is very slightly less than that of the dynamic viscosity.
The primary component of the detergent composition of the present invention is a surfactant system comprising a mixture of amine oxide having alkyl group of average chain length C₁₄―C₁₆ and a predominantly linear anionic surfactant containing an acyclic moiety of more than 12 and less than 18 carbon atoms.
Amine oxides suitable for the purposes of the present invention have the general formula
wherein R, is an alkyl group having an average chain length of from 14 to 16 carbon atoms which can be linear or which can contain up to 70% by weight of the group of methyl or ethyl branching and R₂ and R₃ are C₁-C₄ alkyl or C₁-C₄ hydroxy alkyl groups. The R₁ group can be completely linear, as in material derived from natural fats and oils such as coconut and palm kernel oils, or may be branched as in material derived synthetically from petroleum sources. For the purposes of the invention, up to 70% by weight of the alkyl group R, can contain methyl or ethyl branching, most of which is normally in the 2-position. Suitable sources of this type of alkyl group are alcohols produced by oxo synthesis which have either 40-50% methyl branching or 10-25% methyl branching, dependent on the catalyst employed. Most preferred are alkyl groups having a low level (<25%) of methyl branching.
The R₂ and R₃ groups are normally methyl or hydroxyethyl with the former being preferred.
Anionic surfactants useful in the compositions of the present invention are those incorporating an aliphatic hydrocarbyl moiety having an average carbon chain length of more than 12 and less than 18 atoms, said moiety comprising at least 40% by weight of the anionic surfactant. Suitable anionic surfactants satisfying this constraint include alkanoates, C₁―C₅ alkyl esters of a sulphonated alkanoic acids, olefin sulphonates, alkyl benzene sulphonates in which the alkyl group is a mixture of alkyl moieties containing from 11 to 13 carbon atoms, s-alkane sulphonates, alkyl sulphates, certain alkyl polethoxy sulphates, alkyl phosphates and certain alkyl ether phosphates. Mixtures of any of these surfactants can also be employed if desired. Preferred alkanoates are the C₁₂-C₁₄ alkali metal or alkaline earth metal soaps and mixtures thereof derived from e.g. coconut or palm kernel oils. The preferred a sulphonated alkanoic acid esters are alkali metal sulphonate salts of methyl, ethyl, propyl, and butyl esters of C₁₂―C₁₄ alkanoic acids. Preferred olefin sulphonates are the alkali metal C_12―C₁₄ olefin sulphonates and the alkyl benzene sulphonates are preferably those with a linear alkyl chain.
The alkyl sulphates may be primary or secondary in type, the alkyl group being derived from primary or secondary alcohols. In turn these alcohols may be derived from any of the sources described above in connection with the long chain group of the amine oxide. The average number of ethoxy groups should not exceed 3 per mole where the alkyl chain length is from 12 to 14 carbon atoms and 4 per mole where the alkyl chain length is from 14 to 16 carbon atoms. The cation is normally alkali metal, such as sodium, potassium, lithium, or ammonium, although for certain surfactants, alkaline earth metals such as magnesium can also be used.
Preferred anionic surfactants are primary alkyl sulphates with up to approximately 50% methyl branching, s-alkane sulphonates and alkyl benzene sulphonates. Soaps are also preferred anionic surfactants in mixtures in which the amine oxide:anionic surfactant weight ratio is >20:1.
The surfactant system comprises a combination of the amine oxide and anionic surfactants in a mixture composed of from 93.5% and 99.5% amine oxide and from 0.5% to 6.5% anionic surfactant. From 1% to 1.5% by weight of the composition of this mixture is sufficient to provide a viscosity of 0.18 Pa - s. In the most preferred embodiments of the invention the surfactant mixture comprises from 95.0% to 99.0% of amine oxide and from 1.0% to 5% of anionic surfactant. The applicants have found that the use of a C₁₂―C₁₈ saturated or unsaturated fatty acid salt as the anionic surfactant is very effective in producing a viscosity of >0.18 Pa. s. provided that the fatty acid salt comprises no more than approximately 5% of the surfactant mixture. Fatty acid salt levels in excess of approximately 5% by weight of the mixture give rise to the formation of a gel which is difficult to dispense from a container and apply to a non horizontal surface and is less acceptable aesthetically.
The surfactant systems described above display a viscosity-temperature relationship that has a parabolic profile with the maximum viscosity being exhibited at a temperature in the range of from 0°C to 30°C. An increase in chain length of the R₁ group increases the temperature at which this peak occurs while a reduction in R, chain length and/or branching in the R₁ group reduces the temperature at which the maximum viscosity is produced by the system. A similar effect is seen for variations in chain length and linearity of the lipophilic aliphatic group of the anionic surfactant. Ideally, the viscosity of the composition should be independent of the temperature over a temperature range which encompasses the conditions normally encountered in domestic usage i.e. from 5°C to 25°C. The Applicants have found that this ideal is approached most closely by a surfactant system employing a blend of specific amine oxides, as the respective amine oxide-anionic surfactant combinations display a peak viscosity at different temperatures.
The other essential component of the composition is at least one ionisable non surface-active organic, or inorganic compound which is present in an amount such that the ionic strength of the composition is at least 3.5 moles/dm³.
The ionisable compound(s) can be inorganic in nature e.g. hydroxide, sulphate, halide (particularly chloride) carbonate, nitrate, orthophosphate, pyrophosphate, polyphosphate or silicate, or organic such as citrate, formate, acetate or succinate. In a preferred aspect of the invention, the hypochlorite itself, together with the sodium hydroxide, chloride and chlorate associated with the bleach provides the, or a major proportion of the ionisable compounds required by the invention. In the preferred hypochlorite bleach-containing embodiments of the invention, certain inorganic compounds such as silicates, and organic compounds incorporating oxidisable groups are unstable and should be avoided.
The ionic strength of the composition is calculated by means of the expression
where

C, is the molar concentration of the ionic species in g moles/dm³
Z_; is the valency of the species.

The function C,Z,² is calculated for each of the ionic species in solution, these functions are summed and divided by two to give the composition ionic strength.
The ionisable alkali metal compound normally comprises a caustic alkali such as sodium or potassium hydroxide either alone or in admixture with alkali metal salts. The level of sodium hydroxide necessary to provide a total composition ionic strength of 3.5 moles/dm³ where the composition contains only the amine oxide-anionic surfactant mixture would be approximately 8% to 9% by weight of the composition dependent on the density of the solution. More preferably, for product safety reasons, the at least one ionisable compound comprises a mixture of a caustic alkali in an amount of from 0.5% to 2% by weight of the composition together with one or more alkali metal salts in an amount of at least 10% by weight, more usually at least 15-20%.
The ionisable alkali metal compound can also include any of the water soluble inorganic and organic builder and sequestrant salts normally. incorporated in such products. Compounds classifiable and well-known in the art as detergent builder salts include the nitrilotriacetates, polycarboxylates, citrates, ortho- and pyro-phosphates, and mixtures of any of these. Metal ion seques- trants include all of the above, plus materials like ethylenediaminetetraacetate, the amino- polyphosphonates and phosphates (DEQUEST)°. A wide variety of poly-functional organic acids and salts is disclosed in European Patent Application Publication No. 0040882 which contains examples of the use of such materials in various cleaning compositions. In general the builder/ sequestrant will comprise from 1% to 25% of the composition. Citric acid (2%-20% as sodium citrate) is a preferred builder.
In the present invention in which a hypochlorite bleach is incorporated, the bleach itself, containing the range of by-product materials previously mentioned, provides a major portion of the ionic strength requirement, viz at least 3.0 moles/dm³ assuming an available chlorine level of 9% in the composition. In practice therefore it is usually only necessary to add alkali metal hydroxide on a total composition basis. In this aspect of the invention the fact that the amine oxide should have an R₁ alkyl chain length in the range 14 to 16 carbon atoms permits the use of low levels of both surfactants and ionisable compounds to obtain the desired viscosity and also minimises the rate of decomposition of the hypochlorite arising from the ionic strength of the solution and from reaction with the surfactant components. These preferred embodiments also utilise the amine oxide component in high weight ratios (20:1 to 40:1) to anionic surfactant components such as alkanoates and alkyl sulphates. In the bleach-containing embodiments it is highly preferred that the anionic surfactant component(s) be free of unsaturation in order to avoid attack by the hypochlorite bleach leading to adverse effects on both bleach level and solution viscosity.
The bleach stable perfume is present at a level of from 0.01% to 0.5% preferably from 0.05% to 0.25% by weight of the composition.
The compositions are made by conventional mixing techniques. Although any order of mixing can be used, presolution of the alkali metal hydroxide and any alkali metal salt is desirable and these are normally added to a solution of the amine oxide and the anionic surfactant. Perfume is then added under high shear agitation together with any additional water to provide the desired product concentration. The alkali metal hypochlorite bleach is added last.
The invention is illustrated in the following examples in which percentages are expressed by weight of the composition unless otherwise stated.
In the examples reference to ingredients have been abbreviated as follows:

C₁₄ alkyl dimethyl amine oxide in which the alkyl group is a predominantly linear C₁₄ (>94%) moiety. Available from Albright & Wilson Ltd as Empigen OH. (Registered Trade Mark) NaC₁₃―C₁₅ AS

Sodium C₁₃―C₁₅ primary alkyl sulphate in which the alkyl group is 67% C,₃ 33% C₁₅ and the alkyl groups contain approximately 50% methyl branching on the 2-carbon atom. Available from Imperial Chemical Industries under the trade Name Synprol Sulphate.

Example 1

A premix was formed by dissolving 4.0g of 50% solution NaOH equivalent to 1% of Finished Product in 67g deionised water. To this preparation was added: 8.7g of 30% (by weight) solution of C₁₄ (myristyl) dimethyl amine oxide, 0.4g of 20% (by weight) solution of sodium C₁₃-C₁₅ Alkyl Sulphate, and 0.1 % of bleach stable perfume. This base stock was then agitated to from a homogeneous mixture. Finally, 120 g NaOCI containing 15.0% by weight of available chlorine (supplied by Ellis & Everard) was added to the base stock and agitation continued to give a single phase composition.
The final composition had the final analysis
The lonic strength I was calculated to be 3.69g mol/dm³, and the product viscosity as measured at 20°C by a Brookfield viscometer using a No. 3 spindle at 100 rpm was 0.300 Pa · s after 24 hours.

Example 2

The procedure of Example 1 was repeated except that the amine oxide level was 1.1 % by weight and the C₁₃―C₁₅ alkyl sulphate surfactant was replaced by sodium laurate at a level to give 0.04% soap in the finished product, the surfactant mixture comprising 96.5% amine oxide and 3.5% soap, an amine oxide:soap ratio of 27.5:1.
The ionic strength of the product was virtually identical to that in Example 1 and the product viscosity was 0.225 Pa - s at 20°C after 24 hours.

Claims

1. An aqueous single phase hypochlorite bleach composition having a viscosity of >0.18 Pa - s at 20°C and comprising from 1.0% to 1.5% by weight of a surfactant system comprising a tertiary amine oxide surfactant having the formula R₁R₂R₃N→O wherein R₁ is an alkyl group having an average chain length of from 14 to 16 carbon atoms which is linear or which contains no more than 70% by weight of the group of methyl or ethyl branching, and R₂ and R₃ are C_l-C₄ alkyl or C₁-C₄ hydroxy alkyl together with at least one ionisable, non surface active organic, or inorganic, compound comprising a mixture of alkali metal hypochlorite, alkali metal hydroxide and alkali metal chloride said composition incorporating from 0.01 % to 0.5% by weight of the composition of a bleach stable perfume and having an ionic strength of at least 3.5 moles/dm³ characterised in that the surfactant system consists of a mixture comprising:

a) from 93.5% to 99.5% by weight of the system of said tertiary amine oxide and from

b) 0.5% to 6.5% by weight of the system of an anionic surfactant salt incorporating an aliphatic moiety having an average carbon chain length of more than 12 and less than 18 atoms, said moiety comprising at least 40% by weight of said anionic surfactant.

2. An aqueous single phase hypochlorite bleach composition according to claim 1 wherein the anionic surfactant is selected from alkali metal or alkali earth metal alkanoates, alkyl sulphates, alkane sulphonates, alkyl benzene sulphonates in which the alkyl portion of the alkyl benzene is a linear moiety containing a mixture of groups having from 11 to 13 carbon atoms and mixtures of any of the foregoing.

3. An aqueous single phase hypochlorite bleach composition according to either one of claims 1 and 2 wherein the alkyl group R₁ incorporates no more than 25% methyl branching.

4. An aqueous single phase hypochlorite bleach composition according to any one of claims 1 to 3 wherein the surfactant system comprises from 95% to 99.0% amine oxide and from 1.0% to 5% of an alkanoate or alkyl sulphate surfactant.

5. An aqueous single phase hypochlorite bleach composition according to any one of claims 1 to 4 wherein the at least one ionisable compound comprises a water soluble inorganic or organic builder and/or sequestrant salt.

6. An aqueous single phase hypochlorite bleach composition according to claim 5 wherein the water soluble builder or sequestrant salt is selected from alkali metal citrate, alkali metal amino polycarboxylate and alkali metal aminophosphonate salts.